Taste buds are multicellular receptor organs of the gustatory system, and are innervated by a discrete set of cranial nerves. For nearly a century, taste buds were believed to form late in embryonic development following induction by nerves. However, recent findings have shifted this view dramatically. Early taste bud development is not dependent upon nerves. Further, taste buds arise via processes intrinsic to the tongue, processes that occur long before taste buds differentiate. Most recently, we have demonstrated that epithelium destined to give to taste buds, the pharyngeal endoderm, receives signals very early, during gastrulation, that initially specify, or direct the fate of, this embryonic tissue. Further, cell-cell interactions within this specified endoderm regulate the subsequent patterning of this epithelium so that it gives rise to a distributed array of taste buds. We are now poised to expand substantially on our earlier model, and test detailed hypotheses concerning these key early events in taste bud development. In this proposal, molecular and cellular mechanisms that first specify (fate is directed but still reversible) and then determine (fate is irreversibly selected) the ability of pharyngeal endoderm to generate taste buds will be assessed. An additional question addressed in this aim is whether the same signals are responsible for both processes (Aim 1). Studies of taste bud patterning will be expanded to the molecular realm, to determine if, based upon suggestive gene expression patterns, the Notch signaling pathway is involved in patterning taste buds (Aim 2). Finally, to meld data from mammalian taste bud development with our own, genes known to be present in developing taste organs of mice will be cloned from axolotls and expression of these gene products will be explored in the developing taste epithelium of axolotls. By comparing gene expression patterns across species, we will identify genes associated in general with taste bud development (Aim 3).